Electric discharge tube comprising a fluorescent screen



M. C. TEVES April 1, 1941.

ELECTRIC DISCHARGE TUBE COMPRISING A FLUORESCENT SCREEN Filed Nov. 2, 1958 INVENTOR MARTEN C. TEl/ES ATZI'ORNEY Patented Apr. 1, 1941 ELECTRIG DISCHARGE TUBE COMPRISING. A FLUORESCENT SCREEN Marten Cornelis 'i'eves, Eindhoven, Netherlands,

assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application November 2, 1938, Serial No. 238,318 In the Netherlands August 7, 1937 3 Claims.

This invention relates to an electric discharge tube comprising a fluorescent screen which consists of a transparent support to which is applied a layer of fluorescent material and on which a layer of metal having a melting point of more than 1800 C. is provided either on the fluorescent material or between the support and the fluorescent material, according to copending United States patent application No. 39,798, filed September 9, 1935, by De Boer et al. for Fluorescent screens.

In the principal application it has been set out that it is very advantageous to use for these conductive layers metals having a high melting point, since these are endowed of the property that even very thin layers of them have a slight absorption of light and yet fairly high conductivity. The invention under view concerns an improvement of the invention disclosed in the principal application and resides in that use is made of a fluorescent screen in which the conductive layer on the fluorescent material or between this material and the substratum consist of rhodium. In fact, rhodium has the important advantage over the other metals entering into ac,- count, whose melting points exceed 1800 C., that it does not oxidise in the air, so that in contradistinction, for instance, to the use of tungsten, molybdenum and similar metals the screen, when using rhodium, can be exposed to the air after manufacture without there being a risk of a decrease in conductivity of these layers.

In describing the invention, reference will be made to the drawing Where there is shown schematically and not to scale in cross-section a fluorescent screen embodying the invention. In the drawing, a support surface I, which may, for example, be the glass wall of a cathode ray tube, has deposited thereon a thin substantially monatomic layer 3 of rhodium. On the layer of rhodium are shown the particles of fluorescent material 5. The rhodium layer provides the necessary conductivity to insure that the screen operates efiiciently.

Indeed, when considering what metals enter into account for use as a conductive material according to the above U. S. patent application Serial No. 39,798, we find, besides rhodium, for instance tungsten, tantalium, molybdenum, boron, hafnium, osmium, iridium and thorium. These metals can be precipitated in very thin layers by vaporisation in a vacuum or applied by so-called cathodic disintegration. With the metals entering first of all into account such as tungsten and molybdenum much care has to be taken that the layers formed do not contact with oxygen, since they would immediately oxidise in this case and areno longer suitable for the purpose aimed at. However, rhodium is entirely devoid of these properties, so that the use of this metal ofiers material advantages over theme of the other metals referred to above. is not necessary to take a large number of precautions after the layer has been applied and secondly it is not necessary to apply the layer in an exhausted space. It will be appreciated that owing thereto rhodium exhibits a very particular effect with respect to the other metals, which would enter into account for use as a conductive material according to the above United States patent application Serial' No. 39,798.

Furthermore, it has been found that rhodium eminently adheres to glass and in addition is entirely resistant to the binders and solvents usedfor fluorescent screens.

What I claim is:

1. A fluorescent screen comprising a smooth transparent support, a highly transparent layer of rhodium deposited thereon, and luminescent material deposited upon the layer of rhodium.

2. A fluorescent screen comprising a smooth transparent support structure, a low light absorbing layer of rhodium deposited upon the transparent support structure and a layer of luminescent material deposited upon the layer of rhodium.

3. A luminescent screen comprising a smooth transparent support structure, a layer of luminescent material, and a highly transparent layer of rhodium interposed between the support structure and the fluorescent material.

MARTEN CORNELIS TEVES.

Firstly it i 

